This paper describes the first demonstration of Doppler detection and data transmission at 140 GHz and 4 Gb/s through the air using a single-chip silicon transceiver at 140 GHz. The transceiver, which consists of a 140-GHz pushpush VCO with a static divide-by-64 chain, a 140-GHz amplitude modulator, a 140-GHz LO amplifier, a fundamental frequency mixer, a 140-GHz LNA, and a variable gain IF amplifier, has a downconversion gain of 30 dB and a noise figure of 12.3 dB. It is fabricated in a 130-nm SiGe BiCMOS technology, occupies an area of 1.44 mm 2 , and consumes 1.5 W.